1. Field of the Invention
The present invention relates to an optical pickup apparatus which can emit a plurality of laser beams with different wavelengths to read recording information from a plurality of types of optical disks having different recording densities.
2. Description of the Related Background Art
Generally, a semiconductor laser device is used as a light source of an optical pickup apparatus for playing an optical information recording medium such as CD, DVD, or the like.
To play back the recording medium, the light emission wavelength and the numerical aperture (NA) of an objective lens of the semiconductor laser device which is used for playing a CD and for playing a DVD are different from each other. For example, in the case of the DVD, the wavelength is equal to 650 nm and the NA is equal to 0.6 and, in the case of the CD, the wavelength is equal to 780 nm and the NA is equal to 0.45.
To play different kinds of discs such as CD, DVD, and the like by one disc player, therefore, an optical pickup apparatus having therein light sources of two wavelengths of 650 nm and 780 nm is being used. FIG. 1 shows an example of the optical pickup apparatus.
According to the optical pickup apparatus shown in FIG. 1, a laser device 1 for emitting a laser beam having a wavelength of 650 nm, a laser device 2 for emitting a laser beam having a wavelength of 780 nm, a synthesizing prism 3, a half mirror 4, a collimator lens 5, and an objective lens 6 are sequentially arranged. Further, a photodetector 7 is arranged on another optical axis which is branched from the half mirror 4. In the construction, since an optical system starting with the synthesizing filter 3 and extending to an optical disc 8 is used in common for the CD and DVD, in both cases, the light emitted from the laser device passes through the synthesizing filter 3 and, thereafter, is guided toward the optical disc 8 along an optical axis Y. The objective lens 6 used here is a lens having double focal points and different focal positions, provided in accordance with the two wavelengths. A spherical aberration which is caused by different thicknesses of surface substrates of the CD and DVD can be, consequently, suppressed.
In the construction, however, since a synthesizing prism or the like is needed, a large number of parts is required and the costs of production are high. Further, because it is necessary to match the positions of the two laser devices and the synthesizing prism, the construction becomes complicated, and it is difficult to make adjustments to the device.
In consideration of the problems, it is an object of the present invention to provide an optical pickup apparatus and a laser diode chip, in which a construction of the apparatus for using a plurality of laser beams having different wavelengths can be simplified and miniaturized.
The optical pickup apparatus of the present invention is an optical pickup apparatus comprising a light emitting device having a plurality of light emitting portions for emitting laser beams having different wavelengths on a substrate, for emitting a laser beam from one light emitting portion selected from the plurality of light emitting portions in the same emitting direction in response to a light emitter selecting instruction; at least one objective lens for converging the laser beam emitted from the light emitting device to irradiate a recording surface of an optical disk; and a lens driving device for moving the objective lens to one position within a plurality of different positions from one another in a radial direction of the optical disk, corresponding to the light emitting portion selected by the light emitter selecting instruction.